Rhode Islanders won't cast ballots for about three months, but a crucial deadline looms for voters this month, according to Secretary of State A. Ralph Mollis.

State law requires voters who are registered as Americans Elect, Democrats, Moderates or Republicans to disaffiliate by June 13 if they plan on voting in a different party’s primary Sept. 11. Voters can change their party affiliation by contacting the board of canvassers in the city or town where they are registered to vote.

Some of the key races where primaries appear to be likely include both of Rhode Island's seats in the U.S. House of Representatives. More than 700,000 Rhode Islanders are registered to vote.

“About half of the state’s voters are affiliated with one of the state’s recognized political parties. This is their last chance to make a change,” Mollis said in a statement. “Independent voters do not have to worry about the deadline. They can cast a ballot in any party’s primary.”

Mollis urges voters who are unsure of their political affiliation to use his website at sos.ri.gov to check their voter registration record.

The disaffiliation deadline is just one of the milestones that is included in a free 24-page guide Mollis created to help voters and candidates navigate this year’s elections. Posted on sos.ri.gov, the “2012 Election Calendar” outlines every crucial step from registering to vote to filing campaign finance reports leading up to the Nov. 6 election.